The innate immune system contains several families of germline-encoded pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), Nod-like receptors (NLRs), RIG-1-like receptors (RLRs), cytosolic DNA sensors (CDSs) and C-type lectins (CLRs) (Newton and Dixit 2012). These receptors recognize microbial components termed pathogen-associated molecular patterns (PAMPs). PAMPs are highly conserved molecular structures on a wide range of pathogens such as bacteria, fungi, parasites and viruses. PAMPs include lipid-based bacterial cell wall components such as lipoproteins and lipopolysaccharides, microbial protein components such as flagellin, and pathogen nucleic acids in the form of double stranded DNA and single or double stranded RNA. In addition some PRRs also recognize ‘self’ ligands known as damage-associated molecular patterns (DAMPs) released from damaged or dying cells and tissues. Cells of the innate immune system respond to PAMPs and DAMPs by producing proinflammatory cytokines, chemokines and co-stimulatory molecules that are involved in clearing the pathogens and damaged-self. Furthermore, innate immune responses essentially shape the downstream adaptive immune responses to generate a more specific and long lasting immunity (Hoebe et al. 2004; Pasare and Medzhitov 2005). As such, harnessing innate immune signalling pathways is a promising therapeutic strategy to fight infections, immune disorders, as well as in diseases such as cancer.
TLRs are the best-studied class of innate immune receptors recognizing a diverse range of lipid-, protein-, nucleic acid-based PAMPs and DAMPs (Kawai and Akira 2011). The engagement of TLRs with their specific ligands leads to the activation of innate immune responses, and evokes adaptive immune responses through the activation of antigen presenting cells (APCs) and by amplifying B- and T-cell effector cells (Pasare and Medzhitov 2005; MacLeod and Wetzler 2007). Several studies have demonstrated that stimulation of TLRs with specific ligands and combinations of, to fine-tune adaptive immune responses. Moreover the aberrant TLR expression in cancer cells and several TLR polymorphisms identified in tumors indicate a role for TLRs in cancer (El-Omar et al. 2008; Kutikhin 2011; Mandal et al. 2012). The infiltration of TLR-expressing immune cells into the tumor microenvironment further implies the significance of TLRs and cancer (Bennaceur et al. 2009; Sato et al. 2009). However, the precise contribution of TLRs in cancer remains to be understood. Activation of TLRs can have opposing roles by either promoting cancer cell apoptosis or promoting tumor progression and survival (Huang et al. 2008). Overall, TLRs are promising targets for the development of new and effective therapeutic agents (Kanzler et al. 2007; Wang et al. 2008; So and Ouchi 2010). Several small molecules agonists of TLRs have been identified for use as immune stimulants to boost immunity against cancer (Meyer and Stockfleth 2008).
The present invention provides a method to stimulate biological activities of TLR7 and/or TLR8 and TLR2 with a single new conjugated molecule in order to treat diseases such as viral infections, immune disorders as well as cancer.